Did this supernova explode twice?

All supernovae are exploding stars. However, the nature of supernova explosions is very different. One type, called supernova type 1a, is a binary star in which one of the two stars is a white dwarf. And while all types of supernovae typically explode in a single explosion, astronomers have discovered something that breaks that notion: a Type 1a supernova that may have exploded twice. Type 1A supernovae occur in binary stars in which one star is a white dwarf and the other star is double to another white dwarf. As the primary white dwarf sucks matter from its secondary companion, it eventually accumulates enough mass to exceed the Chandrasekhar limit. When that happens, it causes a catastrophic explosion. However, a type 1a supernova named SN 2022joj behaves strangely. This led the authors of the new paper to suggest that the supernova may have exploded twice. Additionally, it didn’t have to go beyond Chandrasekhar’s limits to explode.

This article is “SN 2022joj: Possibility of double explosion due to thin helium shell”. Not yet published, available on preprint server arXiv. The lead author is Estefania Padilla Gonzalez of the Department of Physics, University of California, Santa Barbara and Las Cumbres Observatory. Double-exploding stars are rare, but not uncommon. They occur when white dwarfs accumulate layers of helium that ignite. In such an explosion, the white dwarf would not cross the Chandrasekhar limit and the explosion would be relatively weak. Such double-exploding supernovae are called subluminous supernovae. But darkness isn’t the only indication of a double-burst supernova. It exhibits an anomalous light curve, with a red glow appearing 11 days before its maximum brightness. After this peak, it resembles a more typical type 1a supernova. This, along with other aspects of spectroscopy, suggested the authors of the new study that Sn 2202joj may have undergone a double explosion.

Different types of stars at different stages of evolution may have layers or shells of different chemical elements. White dwarfs are no exception and can have helium or hydrogen shells. Most white dwarfs have a hydrogen shell or atmosphere. Not to scale, this illustration shows the onion-like layers of an evolved giant star just before its collapse.In this case, the white dwarf’s companion star has an outer helium envelope, and 2202joj siphons off some of that helium to form its own helium envelope. This could trigger a helium explosion even if the star does not exceed the known Chandrasekhar limit. Importantly, this helium explosion produces another element, a nickel isotope called 56Ni. All of the nickel is visible in spectroscopic analysis of the star.

When the helium shell explodes, not only 56Ni is synthesized. Sends a strong shock wave to a white dwarf. This impact can cause another explosion inside the star, so nature creates double-explosion supernovae. Supernova spectroscopy supports this explanation, the authors say. “Spectroscopically, we find strong agreement between SN 2022joj and a double-explosion model with a white dwarf mass of ~1 M⊙ and a thin He shell of 0.01–0.02 M⊙,” the researchers write. writes. This light curve is typical of a type 1a supernova. Nickel produced by the explosion rapidly decays to a peak brightness, then decreases in brightness and is dominated by decay of cobalt.

The light curve tells astrophysicists a lot about what is happening in the star. This was no exception, and the light curve of SN 2202joj told the team of astronomers studying it a lot. Normally, the light curve of a type 1a supernova looks like this:

However, the SN 2202joj’s light curve is different from the normal Type 1a SN’s light curve. There are two separate peaks, the first one being very red and then rapidly decreasing to blue. The image below compares the light curve of SN 2202joj with the light curves of other SNs and different models of double burst SNs. This image contains a lot of data, but it’s worth a look. This figure from our study shows the color evolution of SN 2022joj compared to other SNe and Sne models in color and time post-explosion. Dashed lines show predictions of different models for double-explosion SNe. Black has 2202 Joj, and other colors are other stars that astrophysicists have studied. Note that both the magenta and blue stars are other doubleburst SNs, but 2202joj is a doubleburst SN with a thin helium shell. Of particular interest is that 2202joj is much redder than other supernovae in its early stages. Photo credit: Gonzales et al. 2023 Researchers aren’t 100% sure it’s a double-blast SN. The initial red color suggests that two explosions occurred, but other evidence is conflicting. “However, the composition of SN 2022joj’s nebular spectrum deviates from what would be expected for a double explosion,” they write. The nebula’s spectrum contains strong Fe III emissions that cannot be explained by double explosions.

“More detailed modeling, such as viewing angle effects, should be included to test whether the double-explosion model can explain the nebula’s spectrum,” they conclude. Supernovae are rare, but they play an important role in nature. They synthesize metals and when they explode they spread into space. Without them, rocky planets like ours would not exist. Type 1a supernovae are important due to their unique role in the universe. Scientists believe they have synthesized most of the iron group elements, from titanium to zinc. Nature creates many fascinating things in the universe, but one of the most impressive is the explosion of stars. A star contains an enormous amount of matter, and when one of them explodes, a supernova releases an enormous amount of energy in a short period of time. It’s no surprise that these objects attract our attention.

More information: , arXiv (2023). DOI: 10.48550/arxiv.2308.06334